1. Field of the Invention
This invention relates to a novel process of making the low sensitivity, high energy and density solid oxidizer 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo[5.5.0.0.sup.5,9 0.sup.3,11 ]-dodecane, also known as "TEX". The process provides several advantages over known processes, including faster reaction times with excellent yields and product purity, making it particularly suitable for large-scale synthesis.
2. Description of the Related Art
The small-scale synthesis of TEX is reported by Boyer et al. in Heterocycles, Vol. 31, No. 3, pp. 479-489 (1990), the complete disclosure of which is incorporated herein by reference. Boyer's process starts with 2,3,5,6-tetrahydroxy-1,4-diformylpiperazine (hereinafter referred to as THDFP) and trimeric glyoxal (dihydrate) added to a 0.degree. C. concentrated sulfuric acid medium, which is stirred and maintained at 10.degree. C. to 15.degree. C. for 5 hours. The reaction mixture is then cooled back down to 0.degree. C., and 100% nitric acid is added dropwise, generating an exothermic reaction. Stirring is resumed for 2 hours while the temperature of the reaction mixture is maintained by cooling at between 0.degree. C. to 10.degree. C. The mixture is then allowed to warm to about 25.degree. C. and stirred for another 45 hours. The mixture is then poured onto ice, and a colorless solid precipitate is collected and washed to give a crude mixture which contains TEX.
Boyer et al. reports that the reaction proceeds in the following manner: ##STR1##
However, the present inventors found that treatment of the THDFP with acid generates monomeric glyoxal equivalent due to decomposition of the THDFP. Not only is the addition of extra amounts of trimeric glyoxal reactant unnecessary, but the present inventors surmised that the additional trimeric glyoxal decomposed in the acid bath to contaminate the final product. As a result, the Boyer et al. process provides low yields of TEX and impure TEX, thus requiring additional purification steps and making the Boyer et al. process unsuitable for scale-up.
Another synthesis route for preparing TEX is disclosed in U.S. Pat. No. 5,498,711, the complete disclosure of which is incorporated herein by reference. According to the '711 patent, TEX is synthesized by reacting 1,4-diformyl-2,3,5,6-tetrahydroxypiperazine and derivatives thereof with a strong acid and a nitrate source. The strong acid and nitrate source of preference are sulfuric acid and nitric acid, respectively. The reaction is exothermic and is allowed to continue for two to three hours. The mixture is then poured onto ice, and a solid precipitate is isolated and washed to give a mixture which contains the TEX.
Although the '711 patent teaches that the reaction can be conducted in the range of from about 50.degree. C. to about 70.degree. C. in temperature, it generally encourages starting the reaction in a bath below this temperature range (with a minor exception in Example 24, which starts the reaction below 55.degree. C.), since the reaction between the hexa-substituted piperazine derivative and the constituents of the concentrated acid medium is exothermic nature. However, it has been discovered by the present inventors that the practice of a decreased temperature at the early stages of the reaction is responsible for relatively low yields of TEX and for the generation of large amounts of NO.sub.x fume off, thus making the reaction more violent and dangerous.
There exists a need for a TEX synthesis procedure which safely controls the exothermic nature of the reaction, which yields TEX in a purity suitable for use in explosive compositions without further purification, and which increases the yield of the TEX obtained.